(1) Field of the Invention
The present invention relates to a passive radar early warning system. More particularly the system eliminates spurious received signals and determines the true bearing of a detected signal.
(2) Description of the Prior Art
There are several type prior art passive early warning receivers. These systems utilize only directional antennas. They do not utilize the benefits that can be derived by combining the use of both omnidirectional and directional antennas. In addition most of passive prior art devices do not attempt to accurately determine direction. The ones that do attempt to determine direction have functional problems. One such prior art system uses only periscope bearing to determine the angle of arrival. If the ship is turning while a person is slowly rotating the periscope antennas, confusion can result. Another difficulty is that of finding the direction of a radar signal in a multisignal environment because one has to remember the particular signal that is of interest. Other disadvantages of prior art systems are low sensitivity due to absence of RF preamplifiers and difficulty in the determination of the highest signal level when listening because the acoustic response of the ear is not linear.